SUFFOLK — The federal government has spent $25 million fighting fires in the Great Dismal Swamp National Wildlife Refuge during the last three years.

The tab, combined with poor air quality felt as far away as Washington, D.C., has the U.S. Fish and Wildlife Service reconsidering how it manages the 111,200-acre refuge.

“We’ve been having some discussions,” said Chris Lowie, the refuge’s manager.

The largest wildfire in Virginia since the state began keeping records, this year’s blaze has scorched nearly 6,400 acres. It started Aug. 4 when lightning struck the refuge’s parched floor.

Much of the charred area also burned in 2008, when logging equipment caught fire and set off a 4,884-acre blaze that lasted four months. Each fire cost $12.5 million, though the bill for the current blaze continues to grow.

Expenses include airfare, lodging and food for hundreds of firefighters, Lowie said. Fish and Wildlife also rented vehicles and construction equipment and paid for helicopters to dump water on the fire, he said.

While the firefighters left weeks ago and much of the equipment has been returned, islands of peat continue to smolder. They are contained and no longer considered a threat to the public, Lowie said.

The fire continues to produce acrid smoke, but not enough to affect large portions of Hampton Roads as it did this summer when the state Department of Environmental Quality routinely warned residents with respiratory problems to stay indoors.

A handful of contractors remain at the refuge rebuilding roads and ditches that were damaged during the fire. Fish and Wildlife, meanwhile, is trying to prevent the spread of invasive species and exploring how it can limit the effects of future wildfires.

“You’re not going to prevent a wildfire out here,” said Lowie, noting that water levels in some parts of the refuge have dropped three feet in October.

A handful of invasive plants, including phragmites, a tall, slender grass that grows in marshes, have taken root in the refuge. They likely arrived via water pumps brought to the refuge from North Carolina to fight the fire, Lowie said.

Fast-growing invasive plants like phragmites can wipe out native species. Fish and Wildlife is considering dropping chemicals from a plane that would kill the phragmites and other invasive plants, he said.

It also wants to gain more control of the 50.5 billion of gallons of water the refuge receives annually from rain, streams and runoff.

A large portion of the water evaporates, especially during hot and dry summer months, Lowie said. But billions of gallons are also lost to a ditch system put in place during the 18th century by a logging company whose leaders included future President George Washington.

Before Fish and Wildlife acquired the swamp in 1972, private owners had up to 115 temporary dams they could engage to flood the ground. Today, the number has dwindled to about 40, Lowie said.

Among the areas without the devices is Interior Ditch, a road where the 2008 and current wildfire burned hundreds of acres.

Fish and Wildlife is also considering raising the water level at Lake Drummond, a 4.6-billion gallon body of water in the center of the refuge.

The U.S. Army Corps of Engineers drains roughly 1 million gallons of water from the lake every time it operates the Dismal Swamp Canal, said Joel Scussel, a corps’ engineer in Norfolk. It usually operates the locks four times per day, allowing an average of 2,000 boaters passage annually between Norfolk and Elizabeth City, N.C.

It limits operations to two times per day during periods of drought or fire, Scussel said.

According to a 1977 agreement with the corps, the lake should not exceed 17.15 feet above sea level. The corps occasionally opens the spillway to the canal — at Fish and Wildlife’s request — to prevent the lake from rising too high, Scussel said.

Fish and Wildlife keeps the water from rising too high to keep the 158 miles of roads open to traffic, Lowie said. They are used, at various times, by the logging industry, outdoorsman and nature enthusiasts, he said.

Amber Soja, a National Institute of Aerospace scientist who works at NASA Langley Research Center in Hampto, studies wildfires. She said the fires are a normal part of the refuge’s life cycle. She noted, however, that the last two have been unusually powerful.

“We need fires in the Dismal Swamp,” she said. “They’ve always been there, they just haven’t burned so deep.”

She attributed their staying power to the peat, which, when burned, emits a more concentrated amount of air pollution than grass or brush fires. While there is evidence that global warming is contributing to wildfires in Canada and other northern areas, she isn’t sure it’s causing a spike in mainland U.S.